This invention relates to an overdrive mechanism for use in an automatic transmission of a vehicle such as an automobile.
More particularly, this invention relates to an overdrive mechanism for an automatic transmission of the type incorporating a hydraulic torque converter disposed between an engine and a change gear mechanism.
The conventional torque converter of an automatic transmission varies the turning force automatically and in a smooth and stepless fashion in accordance with the resistance of the vehicle. However, the conventional torque converter is severely limited in a practical sense because of considerable energy loss arising inevitably from fluid friction during the passage of fluid through the torque converter or from turbulence caused by a drastic change in the direction of flow of the fluid. Should a conventional overdrive device be employed in this type of automatic transmission, no satisfactory improvement in fuel efficiency can be attained because the engine power is transmitted automatically through the torque converter at the time of overdrive.
Accordingly, it is a primary object of this invention to provide a new and improved overdrive mechanism which eliminates the above-described problems of the conventional torque converter transmission.
It is a further object of this invention to provide an overdrive mechanism which mechanically transmits the engine power to the change gear mechanism with an improved fuel efficiency by not passing through the torque converter.
Another object of this invention is to minimize the fluctuations in the rotational force by the torque converter when not required. This usually occurs during a constant high speed operation of the engine for a long period such as in overdrive.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the overdrive mechanism of this invention is for automatic transmissions of the type including a change gear mechanism having an input shaft, and a torque converter having an input element connected to an engine and an output element connected to the shaft, and comprises (1) a planetary gear train including (a) a sun gear affixed to the housing of the automatic transmission, (b) a carrier operatively responsive to the input element of the torque converter, and (c) a ring gear operatively connected to the sun gear and the carrier to thereby be operatively responsive to the input element of the torque converter; (2) overdrive clutch means operatively connected to the shaft of the change gear mechanism and activated in response to the operation of the change gear mechanism for engaging the ring gear whereby the shaft of the change gear mechanism is rotated by movement of the ring gear in response to movement of the input element of the torque converter; and (3) a one-way clutch connecting the output element of the torque converter to the shaft of the change gear mechanism, the one-way clutch decoupling the shaft from the output element when the speed of the shaft exceeds that of the output element.
The invention consists in the novel parts, constructions, arrangements, combinations and improvements shown and described. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the principles of the invention.